1. Field of the Invention
The present invention relates to an engine controller for a work vehicle connected to: an operation position detection sensor configured to detect an operation position of an acceleration manually operating device; a rotational speed sensor configured to detect a rotational speed of an engine; and a fuel injection control unit configured to control a fuel injection amount in the engine.
2. Description of the Related Art
A tractor as one example of work vehicle generally has an acceleration manually operating device (e.g., accelerator hand lever and accelerator pedal), a fuel injection control unit configured to control a fuel injection amount in an engine, and a rotational speed sensor configured to detect a rotational speed of the engine. An engine controller is configured to operate the fuel injection control unit, based on a torque curve characteristic in which a rotational speed of the engine changes along with a change in torque. Such an engine controller has an all-speed governor function, a load control function and a droop control function.
The torque curve characteristic is obtained in advance as a relationship between the rotational speed of the engine and a torque as a parameter for calculating a control amount to be sent to the fuel injection control unit, and stored in a form of a table. From this table, a relationship between a torque for each operation position of the acceleration operating device and an engine rotational speed can be extracted. With this configuration, when the acceleration operating device is shifted to a certain operation position, a control amount of the fuel injection control unit of the engine can be determined with reference to the torque curve characteristic, based on a torque value corresponding to the certain operation position and a detected value at a time point by the rotational speed sensor (actual rotational speed of the engine). Based on this control amount, the fuel injection control unit controls a fuel injection mechanism so that a requested fuel injection amount is attained.
Applicant previously has developed a tractor with a controller utilizing the above-described control technique (see Japanese unexamined patent application publication No. 8-244488). The controller of this tractor calculates a difference between a non-load rotational speed of the engine for an operation position of the acceleration operating device (defined for each operation position) and a detected value by the rotational speed sensor (actual rotational speed of the engine), and the difference in rotational speed is used as an estimation value of a load on the engine. In addition, upon operating a transmission mechanism for traveling, the difference in rotational speed, ultimately the engine load, is utilized (specifically, a predetermined low pressure P3 of the hydraulic clutch is determined based on the difference in rotational speed (see paragraphs [0045]-[0047] and FIGS. 6 and 7 of Japanese unexamined patent application publication No. 8-244488)).
Recently, proposals have been made to introduce to a work vehicle a controller for operating the fuel injection control unit of the engine, which has a control function based on a torque curve characteristic in which a change in rotational speed of the engine along with a change in torque is small, or a torque curve characteristic in which the rotational speed of the engine does not change along with the change in torque, i.e., an isochronous control function. When the isochronous control function is realized, a working device (e.g., roll baler for pasture) using an engine as a power source can be installed, which may otherwise not exert a predetermined performance when the rotational speed of the engine changes. In this case, when various control functions with completely different control configurations, such as a droop control function and an isochronous control function, are to be performed, it is important to appropriately obtain a load on the engine.
Therefore, it would be desirable to provide an engine controller which has a plurality of control modes for controlling a fuel injection control unit, and is capable of appropriately estimating a load on the engine.